Session8 J2ME Low Level User Interface

Outline-session 8 (09-April-2009)

>> Low-Level User Interface-Introduction-Canvas-Graphics

Introduction

>>Two key classes make up the low-level API, Canvas and Graphics.Canvas :

>>it has a specific height and width and is drawn onto to create what the end user will see.>> Whatever is drawn becomes visible on the display. >>The canvas class also provides methods for low-level event handling

Graphics:>>We draw onto a canvas with a Graphics object.>>This class has methods for drawing lines, arcs, rectangles and text. >>This class also includes methods to specify color as well as font preferences.

Canvas

>> Canvas is a subclass of DisplayableCreating Canvas:

>> create a subclass of Canvas, and ask that object be set as the current Displayable.

Canvas

>> Coordinate System--The origin for drawing begins in the upper left corner of the display, location 0,0--x values increase heading to the right, y values increase heading down-- When drawing a line or shape (arc, rectangle, etc.), the thickness (known as the pen) is always 1 pixel wide-- if you request to start a line at 1,1--How many pixels will be "filled" for the entire line segment 1,1 to 3,1?

Canvas

>>Canvas Width and Height

>> Painting on a Canvas:-What differs between a Canvas and the other Displayable objects (Form, TextBox, List and Alert) is where the drawing of the component takes place and who is responsible for the drawing.

Canvas

>>Canvas Paint Methods:

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Canvas

>> Communication with Application Manager :-- When the application manager is about to make a Canvas visible on the display, it will call the method showNotify().-- When the Canvas has been removed from the display, the method hideNotify() is called

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Canvas

>> Communication with Application Manager :-- When the application manager is about to make a Canvas visible on the display, it will call the method showNotify().-- When the Canvas has been removed from the display, the method hideNotify() is called

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Canvas

>> Event Handling:--The low-level interface, consisting of key codes, game actions and pointer events.Commands:• addCommand(Command)• isShown()• removeCommand(Command)• setCommandListener(CommandListener)

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Canvas

>> Key Codes:--Key codes are numeric values that map directly to specific keys on a mobile device.--These codes correspond to the ITU-T keypad (0–9, *, #) the standard telephone keypad

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Canvas

>> Key Codes:

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Canvas

>> Game Actions:--MIDP defines a set of constants, referred to as game actions, to facilitate event handling for game related events.--You are assured that each game action will be assigned a key code by the implementationSample:GameAction.java

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Canvas

Canvas

>> pointer events:-- The MID Profile includes a set of methods to interact with pointer devices such as a mouse or touch screen.

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